Analog flow rate measuring and controlling units are known with which differential pressure measurement is effected by way of an orifice in a flow channel to determine the rate of flow. Following that, the value obtained by this measurement is compared with a desired value in a calculating unit. If the actual value differs from the desired value specified the calculating unit emits a correcting signal for application to a proportional valve unit which then initiates a correcting process to cause the measured value of the flow rate to coincide with the desired value.
A problem with the known flow rate measuring and controlling means is that they are relatively inflexible and cannot readily be matched to changes occuring in system components. Processing of the measurement and control data is substantially predetermined by the system components. While the digital components in their signal processing, fundamentally, are quite free of variations of operating parameters which may occur in the course of operation (e.g. due to aging of the components, thermal drifts, etc.), the sensors, analog amplifiers, analog comparators, and the like are influenced by such drifts.